Abstract: This report deals with phase transition in Bond Fluctuation Model (BFM) of a linear hom... more Abstract: This report deals with phase transition in Bond Fluctuation Model (BFM) of a linear homo polymer on a two dimensional square lattice. Each monomer occupies a unit cell of four lattice sites. The condition that a lattice site can at best be a part of only one monomer ensures self avoidance and models excluded volume effect. We have simulated polymers with number of monomers ranging from 10 to 50 employing Boltzmann and non-Boltzmann Monte Carlo simulation techniques.
Abstract: Interacting Growth Walks is a recently proposed stochastic model for studying the coil-... more Abstract: Interacting Growth Walks is a recently proposed stochastic model for studying the coil-globule transition of linear polymers. We propose a flat energy histogram version for Interacting Growth Walk. We demonstrate the algorithm on two dimensional square and triangular lattices by calculating the density of energy states of Interacting Self Avoiding Walks.
Abstract We present an exactly solvable mean-field-like theory of correlated ternary sequences wh... more Abstract We present an exactly solvable mean-field-like theory of correlated ternary sequences which are actually systems with two independent parameters. Depending on the values of these parameters, the variance on the average number of any given symbol shows a linear or a superlinear dependence on the length of the sequence. We have shown that the available phase space of the system is made up of a diffusive region surrounded by a superdiffusive region.
Abstract: A brief introduction to the technique of Monte Carlo simulations in statistical physics... more Abstract: A brief introduction to the technique of Monte Carlo simulations in statistical physics is presented.
Monte Carlo methods have emerged as a powerful and reliable tool for simulating several complex p... more Monte Carlo methods have emerged as a powerful and reliable tool for simulating several complex phenomena in statistical physics, see, eg, Refs. 1, 2. The Metropolis algorithm 3 discovered in the middle of the last century can be considered as the starting point. This algorithm generates a Markov chain, the asymptotic part of which contains microstates belonging to a canonical ensemble at a temperature chosen for the simulation.
A length dependence of the effective mobility in the form of a power law, B∼ L1− 1/α, is observed... more A length dependence of the effective mobility in the form of a power law, B∼ L1− 1/α, is observed in dispersive transport in amorphous substances, with 0< α< 1. We deduce this behavior as a simple consequence of the statistical theory of extreme events. We derive various quantities related to the largest value in samples of n trials, for the exponential and power-law probability densities of the individual events.
Abstract: An introduction to the basics of Monte Carlo is given. The topics covered include, samp... more Abstract: An introduction to the basics of Monte Carlo is given. The topics covered include, sample space, events, probabilities, random variables, mean, variance, covariance, characteristic function, chebyshev inequality, law of large numbers, central limit theorem (stable distribution, Levy distribution), random numbers (generation and testing), random sampling techniques (inversion, rejection, sampling from a Gaussian, Metropolis sampling), analogue Monte Carlo and Importance sampling (exponential biasing, spanier technique).
Abstract: A review of Bayesian restoration of digital images based on Monte Carlo techniques is p... more Abstract: A review of Bayesian restoration of digital images based on Monte Carlo techniques is presented. The topics covered include Likelihood, Prior and Posterior distributions, Poisson, Binay symmetric channel, and Gaussian channel models of Likelihood distribution, Ising and Potts spin models of Prior distribution, restoration of an image through Posterior maximization, statistical estimation of a true image from Posterior ensembles, Markov Chain Monte Carlo methods and cluster algorithms.
We show that the Density of States (DoS) for lattice Self Avoiding Walks can be estimated by usin... more We show that the Density of States (DoS) for lattice Self Avoiding Walks can be estimated by using an inverse algorithm, called flatIGW, whose step-growth rules are dynamically adjusted by requiring the energy histogram to be locally flat. Here, the (attractive) energy associated with a configuration is taken to be proportional to the number of non-bonded nearest neighbor pairs (contacts).
ABSTRACT In this paper, an artificial neural network (ANN) model has been suggested to predict th... more ABSTRACT In this paper, an artificial neural network (ANN) model has been suggested to predict the constitutive flow behavior of a 15Cr-15Ni-2.2 Mo-Ti modified austenitic stainless steel under hot deformation. Hot compression tests in the temperature range 850 C-1250 C and strain rate range 10-3-102 s-1 were carried out. These tests provided the required data for training the neural network and for subsequent testing. The inputs of the neural network are strain, log strain rate and temperature while flow stress is obtained as output.
Radiation streaming through ducts is an important and difficult problem in nuclear reactor shield... more Radiation streaming through ducts is an important and difficult problem in nuclear reactor shielding. Methods of computing the streaming flux through straight cylindrical ducts have been reviewed profusely by many people-1-"^. Only a few attempts have been made in the study of radiation streaming through annular cylindrical ducts. This problem is of importance in reactor shielding, where one encounters cylindrical plugs with annular gaps all around.
The present study aims at evaluating the relative accuracies with which the different approximati... more The present study aims at evaluating the relative accuracies with which the different approximations to the transport theory represent the spatial and spectral distribution of neutrons in a typical fast reactor shield. Diffusion, removal diffusion and discrete ordinate transport calculations, with and without the inclusion of anisotropic scattering effects, have been performed for the lateral and axial shield configurations of the French fast reactor Rapsodie.
We investigate the lifetime distribution P (τ, t) in one and two dimensional coarsening processes... more We investigate the lifetime distribution P (τ, t) in one and two dimensional coarsening processes modelled by Ising–Glauber dynamics at zero temperature. The lifetime τ is defined as the time that elapses between two successive flips in the time interval (0, t) or between the last flip and the observation time t. We calculate P (τ, t) averaged over all the spins in the system and over several initial disorder configurations.
Abstract: We present an exact enumeration study of short SAWs in two as well as three dimensions ... more Abstract: We present an exact enumeration study of short SAWs in two as well as three dimensions that addresses the question,what is the shortest walk for which the existence of all the three phases-coil, globule and the {\ it theta}-could be demonstrated'. Even though we could easily demonstrate the coil and the globule phases from Free Energy considerations, we could demonstrate the existence of a {\ it theta} phase only by using a scaling form for the distribution of gyration radius.
Abstract: Nematic liquid crystals confined to geometrically as well as chemically patterned subst... more Abstract: Nematic liquid crystals confined to geometrically as well as chemically patterned substrate on one end and a flat substrate with strong anchoring on the other is studied using non-Boltzmann Monte Carlo methods. We observe significant deviations from the continuum-based predictions of the phase diagram which was studied as a function of tilt angle at the top substrate and thickness of the cell. Onset of biaxiality at larger tilt angles at the top substrate is observed.
The confining effect of a spherical substrate inducing anchoring (normal to the surface) on rod-l... more The confining effect of a spherical substrate inducing anchoring (normal to the surface) on rod-like liquid crystal molecules contained in a thin film spread over it has been investigated with regard to possible changes in the nature of the isotropic-to-nematic phase transition as the sample is cooled.
Abstract We propose a soft-output detection scheme for multiple-input-multiple-output (MIMO) syst... more Abstract We propose a soft-output detection scheme for multiple-input-multiple-output (MIMO) systems. The detector employs Markov chain Monte Carlo method to compute bit reliabilities from the signals received and is thus suited for coded MIMO systems. It offers a good trade-off between achievable performance and algorithmic complexity.
The interacting growth walk (IGW) is a kinetic algorithm proposed recently for generating long, l... more The interacting growth walk (IGW) is a kinetic algorithm proposed recently for generating long, lattice polymer configurations. The growth process in IGW is tuned by a parameter called the growth temperature TG= 1/(kBβG). In this paper we consider IGW on a honeycomb lattice. We take the non-bonded nearest neighbour contact energy as ε=− 1. We show that at βG= 0, IGW algorithm generates a canonical ensemble of interacting self-avoiding walks at β= β ̂ (β G= 0)= ln (2).
Abstract: This report deals with phase transition in Bond Fluctuation Model (BFM) of a linear hom... more Abstract: This report deals with phase transition in Bond Fluctuation Model (BFM) of a linear homo polymer on a two dimensional square lattice. Each monomer occupies a unit cell of four lattice sites. The condition that a lattice site can at best be a part of only one monomer ensures self avoidance and models excluded volume effect. We have simulated polymers with number of monomers ranging from 10 to 50 employing Boltzmann and non-Boltzmann Monte Carlo simulation techniques.
Abstract: Interacting Growth Walks is a recently proposed stochastic model for studying the coil-... more Abstract: Interacting Growth Walks is a recently proposed stochastic model for studying the coil-globule transition of linear polymers. We propose a flat energy histogram version for Interacting Growth Walk. We demonstrate the algorithm on two dimensional square and triangular lattices by calculating the density of energy states of Interacting Self Avoiding Walks.
Abstract We present an exactly solvable mean-field-like theory of correlated ternary sequences wh... more Abstract We present an exactly solvable mean-field-like theory of correlated ternary sequences which are actually systems with two independent parameters. Depending on the values of these parameters, the variance on the average number of any given symbol shows a linear or a superlinear dependence on the length of the sequence. We have shown that the available phase space of the system is made up of a diffusive region surrounded by a superdiffusive region.
Abstract: A brief introduction to the technique of Monte Carlo simulations in statistical physics... more Abstract: A brief introduction to the technique of Monte Carlo simulations in statistical physics is presented.
Monte Carlo methods have emerged as a powerful and reliable tool for simulating several complex p... more Monte Carlo methods have emerged as a powerful and reliable tool for simulating several complex phenomena in statistical physics, see, eg, Refs. 1, 2. The Metropolis algorithm 3 discovered in the middle of the last century can be considered as the starting point. This algorithm generates a Markov chain, the asymptotic part of which contains microstates belonging to a canonical ensemble at a temperature chosen for the simulation.
A length dependence of the effective mobility in the form of a power law, B∼ L1− 1/α, is observed... more A length dependence of the effective mobility in the form of a power law, B∼ L1− 1/α, is observed in dispersive transport in amorphous substances, with 0< α< 1. We deduce this behavior as a simple consequence of the statistical theory of extreme events. We derive various quantities related to the largest value in samples of n trials, for the exponential and power-law probability densities of the individual events.
Abstract: An introduction to the basics of Monte Carlo is given. The topics covered include, samp... more Abstract: An introduction to the basics of Monte Carlo is given. The topics covered include, sample space, events, probabilities, random variables, mean, variance, covariance, characteristic function, chebyshev inequality, law of large numbers, central limit theorem (stable distribution, Levy distribution), random numbers (generation and testing), random sampling techniques (inversion, rejection, sampling from a Gaussian, Metropolis sampling), analogue Monte Carlo and Importance sampling (exponential biasing, spanier technique).
Abstract: A review of Bayesian restoration of digital images based on Monte Carlo techniques is p... more Abstract: A review of Bayesian restoration of digital images based on Monte Carlo techniques is presented. The topics covered include Likelihood, Prior and Posterior distributions, Poisson, Binay symmetric channel, and Gaussian channel models of Likelihood distribution, Ising and Potts spin models of Prior distribution, restoration of an image through Posterior maximization, statistical estimation of a true image from Posterior ensembles, Markov Chain Monte Carlo methods and cluster algorithms.
We show that the Density of States (DoS) for lattice Self Avoiding Walks can be estimated by usin... more We show that the Density of States (DoS) for lattice Self Avoiding Walks can be estimated by using an inverse algorithm, called flatIGW, whose step-growth rules are dynamically adjusted by requiring the energy histogram to be locally flat. Here, the (attractive) energy associated with a configuration is taken to be proportional to the number of non-bonded nearest neighbor pairs (contacts).
ABSTRACT In this paper, an artificial neural network (ANN) model has been suggested to predict th... more ABSTRACT In this paper, an artificial neural network (ANN) model has been suggested to predict the constitutive flow behavior of a 15Cr-15Ni-2.2 Mo-Ti modified austenitic stainless steel under hot deformation. Hot compression tests in the temperature range 850 C-1250 C and strain rate range 10-3-102 s-1 were carried out. These tests provided the required data for training the neural network and for subsequent testing. The inputs of the neural network are strain, log strain rate and temperature while flow stress is obtained as output.
Radiation streaming through ducts is an important and difficult problem in nuclear reactor shield... more Radiation streaming through ducts is an important and difficult problem in nuclear reactor shielding. Methods of computing the streaming flux through straight cylindrical ducts have been reviewed profusely by many people-1-"^. Only a few attempts have been made in the study of radiation streaming through annular cylindrical ducts. This problem is of importance in reactor shielding, where one encounters cylindrical plugs with annular gaps all around.
The present study aims at evaluating the relative accuracies with which the different approximati... more The present study aims at evaluating the relative accuracies with which the different approximations to the transport theory represent the spatial and spectral distribution of neutrons in a typical fast reactor shield. Diffusion, removal diffusion and discrete ordinate transport calculations, with and without the inclusion of anisotropic scattering effects, have been performed for the lateral and axial shield configurations of the French fast reactor Rapsodie.
We investigate the lifetime distribution P (τ, t) in one and two dimensional coarsening processes... more We investigate the lifetime distribution P (τ, t) in one and two dimensional coarsening processes modelled by Ising–Glauber dynamics at zero temperature. The lifetime τ is defined as the time that elapses between two successive flips in the time interval (0, t) or between the last flip and the observation time t. We calculate P (τ, t) averaged over all the spins in the system and over several initial disorder configurations.
Abstract: We present an exact enumeration study of short SAWs in two as well as three dimensions ... more Abstract: We present an exact enumeration study of short SAWs in two as well as three dimensions that addresses the question,what is the shortest walk for which the existence of all the three phases-coil, globule and the {\ it theta}-could be demonstrated'. Even though we could easily demonstrate the coil and the globule phases from Free Energy considerations, we could demonstrate the existence of a {\ it theta} phase only by using a scaling form for the distribution of gyration radius.
Abstract: Nematic liquid crystals confined to geometrically as well as chemically patterned subst... more Abstract: Nematic liquid crystals confined to geometrically as well as chemically patterned substrate on one end and a flat substrate with strong anchoring on the other is studied using non-Boltzmann Monte Carlo methods. We observe significant deviations from the continuum-based predictions of the phase diagram which was studied as a function of tilt angle at the top substrate and thickness of the cell. Onset of biaxiality at larger tilt angles at the top substrate is observed.
The confining effect of a spherical substrate inducing anchoring (normal to the surface) on rod-l... more The confining effect of a spherical substrate inducing anchoring (normal to the surface) on rod-like liquid crystal molecules contained in a thin film spread over it has been investigated with regard to possible changes in the nature of the isotropic-to-nematic phase transition as the sample is cooled.
Abstract We propose a soft-output detection scheme for multiple-input-multiple-output (MIMO) syst... more Abstract We propose a soft-output detection scheme for multiple-input-multiple-output (MIMO) systems. The detector employs Markov chain Monte Carlo method to compute bit reliabilities from the signals received and is thus suited for coded MIMO systems. It offers a good trade-off between achievable performance and algorithmic complexity.
The interacting growth walk (IGW) is a kinetic algorithm proposed recently for generating long, l... more The interacting growth walk (IGW) is a kinetic algorithm proposed recently for generating long, lattice polymer configurations. The growth process in IGW is tuned by a parameter called the growth temperature TG= 1/(kBβG). In this paper we consider IGW on a honeycomb lattice. We take the non-bonded nearest neighbour contact energy as ε=− 1. We show that at βG= 0, IGW algorithm generates a canonical ensemble of interacting self-avoiding walks at β= β ̂ (β G= 0)= ln (2).
Growth is a natural process by which a system, for example, a tree, acquires a history-dependent ... more Growth is a natural process by which a system, for example, a tree, acquires a history-dependent (or a causal) structure. Since a growing tree is never ungrown, its growth is an irreversible process. A generic but informal description of its structural features evolves from repeated observations of a variety of structural forms that these systems acquire during their natural growth. Whether it is also a meaningful statistical description depends on whether the collection of such irreversibly grown structures is amenable to a statistical mechanical study.
Non-Boltzmann sampling techniques like the recent Wang-Landau algorithm [1] estimate directly the... more Non-Boltzmann sampling techniques like the recent Wang-Landau algorithm [1] estimate directly the density of states (DoS) for a given Hamiltonian. This is achieved by making the system take random walk in the microstate space, leading asymptotically to a uniform distribution in energy space, through appropriate algorithmic guidance.
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